1. Field of the Invention
The invention relates to an adaptive lighting apparatus for high-speed image recordings for an object by means of a number of high-speed image recording devices. Furthermore, the present invention relates to a method for calibrating such a lighting apparatus.
2. Description of the Related Art
The change in light source technology that has been apparent for some time, particularly in respect of the significant increase in power from light emitting diodes, can be seen not just in motor vehicle exterior lighting. Light emitting diodes are now frequently used as room lighting too and as technical lighting sources. Although initial applications in which extreme brightness requirements apply, such as the lighting of safety trial scenes when examining and simulating motor vehicle accidents, are being discussed, they are currently still right at the start of their technological application.
Vehicle safety has a high level of significance for the development of motor vehicles. Therefore, crash trials, crash simulations or the checking of safety-relevant components of a motor vehicle in appropriately designed simulation arrangements involve(s) the use of special high-speed image recording devices that typically have recording frequencies of between 1000 and 2000 frames per second in order to allow as many details as possible to be recorded, so that the crash behavior can be analyzed very precisely. At such high recording speeds, avoiding any motion blur requires short exposure times that are typically between 200 and 400 microseconds.
If the distance covered by the moving object to be examined (motor vehicle) during performance of the trial—particularly taking account of the depiction scale—is shorter, within the shutter opening time of the high-speed image recording device, than the interval between two adjacent light-sensitive sensor points (sensor pixels) of an image capture sensor means of the high-speed image recording device, movement of the object is no longer discernible. Therefore, it is no longer possible to observe any motion blur either. The setting of the exposure time of the high-speed image recording device therefore forms a suitable compromise between the avoidance of undesirable motion blur and a maximum exposure time, so that it is possible to have sufficient incidence of photons on the image capture sensor means of the high-speed image recording device, and hence sufficient image brightness can be achieved. Besides the exposure time, a further variable is the aperture value of an aperture means of the high-speed image recording device, which likewise has a direct influence on the resulting depth of focus.
To meet the aforementioned requirements of high-speed image recording devices, the lighting apparatus used to illuminate the object during image recording must—at image recording frequencies in the aforementioned order of magnitude—produce a very high luminous flux so that the object can be illuminated to a sufficient extent. The lighting intensity at the object is typically in an order of magnitude of approximately 80 000 to 160 000 lux for a luminous flux of approximately 2.5 to 5.5 Mlm (megalumens). If such a large quantity of light is shone onto the object on trial (test vehicle with trial setup), there are not only illuminated regions but also relatively pronounced regions of shade. The light from the lighting apparatus that is reflected by the object results in different bright/dark profiles in different spatial directions.
A simulation arrangement for motor vehicle accidents is disclosed in DE 198 26 288 B4, for example.
The invention is based on the object of providing a lighting apparatus of the type cited at the outset and also a method for calibrating such a lighting apparatus that can be used to achieve particularly homogeneous illumination of an object that needs to be lit for high-speed image recordings.